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Always-available Static and Dynamic Feedback

Developers who write code in a statically typed language are denied the ability to obtain dynamic feedback by executing their code during periods when it fails to type-check. They are further confined to the static typing discipline during times in the development process where it does not yield the highest productivity. If they opt instead to use a dynamic language, they forgo the many benefits of static typing. We present a novel approach to giving developers the benefits of both static and dynamic typing, throughout the development process, and without the burden of manually separating their program into statically- and dynamically-typed parts.

Our approach relaxes the static type system and provides a semantics for many type-incorrect programs. We implemented our approach in a publicly available tool, DuctileJ, for the Java language. In case studies, DuctileJ conferred benefits both during prototyping and during the evolution of existing code.